Reclaiming waste products in the manufacture of sulfite fiber.



H. K. MOORE & R. B. WOLF. BEGLAIMING WASTE PRODUCTS IN THE MANUFACTURE OF SULIITB FIBER.

APPLIOATION FILED NOV. 1, 1910.

Patented July 14,1914;

r l l I l l l l l l l I I l 1 l l l l I UNITED STATES PATENT OFFIiGE.

HUGH K. MOORE AND ROBERT 1B. WOLF, OF' BERLIN, NEW HAMPSHIRE.

Specification of Letters Patent.

Patented July 14, 1914.

Application filed November 1, 1910. Serial No. 580,158.

To all whom it may concern Be it known that we, HUGH K. MOORE and ROBERT B. WOLF, of Berlin, in the county of Coos and State of New Hampshire, have invented certain new and useful Improvements in Reclaiming Waste Products in the Manufacture of Sulfite Fiber, of which the following is a specification.

In the manufacture of sulfite fiber in which the ground or chipped wood is treated with acid to dissolve the lignin and cementitious materials of the wood and free the cellulose fiber, it has generally been customary, after the cooking operation to blow the digester, or discharge the contents thereof into a blow pit equipped with a vomit stack so called, which permits the escape of the vapor and gases. These vapors and gases compose free sulfur dioxid, water, wood alcohol, benzaldehyde, acetone, acetic acid and various by-products, all of which heretofore escaped into the atmosphere.

The object of the present invention is the reclamation of some of the waste products which have heretofore been discharged with the vapor or steam from the blow pit.

In carrying out our invention, we conduct the vapors arising from the pit into contact with a chilled solid body to condense the water vapor and those other vapors which will condense at slightly less than the boil ing point of water, and thereby to separate them from sulfur dioxid and such waste inert gases as may be discharged. The sulfur dioxid is then recovered in suitable form for reuse. The products of condensation are collected, and may be further treated for the recovery of valuable byproducts therein contained. By withdrawing these products of condensation from the surface condenser at ap roximately the boiling point of water, the a sorption thereby of sulfur dioxid is materially prevented.

On the accompanying drawing, we have illustrated certain of the instrumentalities which may be utilized in carrying out our process.

The digester is illustrated at 1 and is of the type used in the manufacture of sulfite fiber. In it are placed the chips and the acid, and, after the neck is sealed, steam is injected into the digester to bring the contents thereof to the proper temperature. If desired, sulfur dioxid may be injected into the digester in accordance with the process described in our application Serial No. 451,246, filed February 1, 1910. After the wood has been cooked at the proper temperature for the proper length of time and the cellulose fibers have been freed from their cementing materials, the contents of the digester are blown in the usual way through the pipe 2 into a blow pit which is conventionally illustrated at 3 but which is constructed as ordinarily with the false bottom, not shown, for permitting the escape ofthe waste liquors. As usual, the interior of the blow pit is at slightly .less than atmospheric pressure. Hence when the contents of a digester of ordinary size are discharged into the blow pit, at a steam pressure of say from 45 to 7 5 pounds per square inch (not including the pressure due to the static head), from 18,000 to 20,000 pounds of steam are liberated in the blow pit from the discharged Water. The temperature of the contents of the digester varies from 250 F. to 320 'F., and, as soon as thematerials reach the blow pit, vapors arise therefrom and are conducted away through the vomit stack 4. Heretofore in actual practice these stacks have always opened into the atmosphere into which the risin 'vapors escape and become dissipated. In addition to the vapors, there has been heretofore an escape of a certain amount of free sulfur dioxid which was not utilized in the cooking operation. In accordance with our process, the vomit stack is closed to the atmosphere and the vapors and gases are conducted to a surface condenser conventionally illustrated at 5. The surface condenser may be of any suitable or desired type. As illustrated, it is provided with diaphragms 6 6 forming compartments 7, 8, and 9, the compartments 7 and 9 communicating through tubes'10 passed through the chamber 8. As shown, the vomit stack discharges into the compartment 8 and the gases and va ors are caused to circulate around the tu es. Cold water or any other suitable cooling medium is introduced through a pipe 11 to the chamber 7, and, passing through the tubes to the chamber 9, is discharged through the circulating pipe 12. The vapors, entering the condenser from the vomit stack, are condensed and pass therefrom by a pipe 13 to a receptacle 14 fro n which they may be drawn by the valveddischarge pipe 15. Ordinarily we employ water for the cooling medium at its seasonable temperatures, although in lieu thereof a chilled cooling medium might be utilized, or the water itself might be' cooled ing vapors from blowing digesters, while herein described as applying to.the sulfite process may also be applied to any other process such as the so called sulfate and soda process.

The condensation of the water vapor to water permits the absorption by the water of only a certain relatively small portion of the free sulfur dioxid gas which escapes with the vapor. The remaining largevolume of S0 is conducted from the con-.

denser by means of the trapped pipe 16, through a tank or receptacle 17 which contains a body of suit-able absorbent such as sodium hydrate (NaOI-I), calcium hydrate (-CaO H etc. To the upper end of the receptacle is connected an exhaust pipe 18 leading to a vacuum pump indicated at 19.

The unabsorbed sulfur dioxid, leaving the condenser, is drawn by the vacuum apparatus into the absorber 16 where 1t is wholly absorbed by the sodium hydrate or other absorbent material.

The product of the condensation, which is collected in the tank 14 maybe neutralized with calcium hydroxid Ca(OI-I) This has the effect of precipitating the S0 in the form of calcium sulfite (CaSO which is removed by passing the materials through a filter press, leaving the filtrate practically clear and neutral. The filtrate contains acetic acid in the form of a lime or other salt, methyl alcohol, benzaldehyde, acetone and other organic acid salts and compounds which may be separated and removed by any of the well known processes. The absorbent in the tank 17 after it has absorbed to its full capacity the sulfur dioxid gas, may be used in making the bisulfite which is used in the digesters in cooking the wood.

In our previous application, hereinbefore identified, we have described a process of reclaiming the sulfur dioxid and other waste products discharged from the relief valves rom the digester. The present invention provides for completely reclaiming the sulfur dioxid which heretofore has been lost in the operation of blowing the digesters into the blow pits. In addition to reclaiming the sulfur dioxid, so that it may be again utilized, the present invention provides for reclaiming and utilizing valuable products such as methyl alcohol, benzaldehyde, acetone, acetic acid and other organic acids and compounds. It is desirable that the products of condensation should be as free as possible of surfur dioxid.

WVe have stated herein that the vapors are condensed by a surface condenser or in other words that the vapors from the blow pit, are condensed by bringing them into contact with a chilled solid surface. In this way the only water which can absorb the sulfur dioxid is that which has been condensed from. the steam which comes from the blow pit, and consequently this water may be brought out so near the boiling point that it contains the minimum amount of the gas. Consequently the greater volume of unconfined gas will not be absorbed by the water but will pass into the absorber at 17. Furthermore by the employment of a surface condenser, the water, which is used as the cooling medium and which is delivered fromthe condenser in a clean heated condition, may be utilized for a variety of purposes for which it could not be used if it had been previously employed in the direct condensation of the vapors by contact therewith, because in the latter case it would have absorbed a portion of the sulfur dioxid. Preferably therefore the water of condensation is maintained at a temperature but slightly less than the boiling point so as to limit the absorption thereby of the free 80,.

It will be understood from the foregoing description, that the instrumentalities for carrying out the process are illustrated diagrammatically on the drawing, and no attempt has been made to show them in their relative proportions or to show them in detail, as their details of construction may be varied as circumstance and convenience dictate.

Having thus explained the nature of'our said invention and described a way of constructing and using the same, although without attempting to set forth all of the forms in which it may be made or all of the modes of its use, what we claim is:

1. The combination with a digester, a blow pit, and a stack communicating with the blow pit to receive the vapors and gases therefrom, of a surface condenser communicating with said stack for condensing the watery vapors, whereby the absorption of the free gases is limited to that by the products of condensation, means for receiving the uncondensed gases, and means for collecting the products of condensation.

2,. The herein described process of recovering sulfur dioxid, which consists in distion, and recovering the remaining sulfur charging the contents of a digester into a dioxid.

blow pit which is maintained at not more In testimony whereof we have afiixed our than substantially atmospheric pressure, signatures, in presence of two Witnesses.

5 separating an recovering t e pulp, con- T x v 9 densing the vapors Without the addition of v ggigg i g Wat-er thereto, whereby the absorption of the sulfur dioxid is limited to that by the liquid Witnesses: products of condensation, conducting away JAMES E. MURRIXER,

l0 separately the liquid product of condensa- FRANK J. GRAY. 

